Preheat oven to 225F and line a large cookie sheet with parchment paper. Set aside.
Combine egg whites, cream of tartar, and salt in a large, completely clean and grease-free bowl.
Using an electric mixer or a stand mixer fitted with the whisk or paddle attachment, stir on low speed until mixture becomes foamy.
Increase speed to high and gradually add sugar, about 1 Tablespoon at a time, stirring after each addition until sugar is dissolved (about 15-20 seconds between each addition).
Beat until mixture is thick, shiny, and has increased in volume. Mixture should have stiff peaks.
Using a spatula, fold in vanilla extract and sifted cocoa powder until completely combined
Fit a large disposable piping bag with a large tip (I used a large star tip) and transfer meringue into prepared piping bag and pipe onto prepared cookie sheet. The meringue cookies can be pretty close to each other as they won’t spread, and you will want to bake all of the cookies at the same time, so make sure you leave enough space.
Bake on 225F for 1 hour. Turn off the oven once the baking time has passed, but do not open the oven door. Leave the oven door closed and allow cookies to cool completely in the oven (1-2 hours) before removing.
Meringue cookies should be crisp and can be stored in an airtight container. Keep away from heat and moisture as it can soften your meringues.
Once cookies have cooled completely, place dark chocolate melting wafers in a small microwave-safe bowl and melt according to instructions on packaging.
Once chocolate has melted, dip meringues halfway into chocolate, remove, and return to baking sheet or transfer to a cooling rack until chocolate has hardened.